The overall incidence of nonanomalous intrauterine growth retardation (IUGR) varies between 6 and 7% of all births. IUGR accounts for 14% of all stillbirths and 6% of all neonatal deaths. Results from autopsies done on these fetuses/newborns, clearly demonstrate that weights of liver, spleen, and kidneys, as well as body length are significantly smaller in these fetuses when compared to normal fetuses/newborns. Brain weights, however, do not show such differences. Thus, there is an asymmetrical organ growth in these nonanomalous IUGR fetuses. This asymmetry in organ growth is thought to occur because of an ALTERATION IN THE DISTRIBUTION of the cardiac output. To date, most of our knowledge regarding the distribution of the combined cardiac output in either the normal or asphyxiated fetus has been obtained from experimental animals using invasive techniques. Data in the human IUGR fetuses are lacking. With recent improvement in ultrasound technique, color pulsed Doppler can be applied to quantify systemic and regional blood flow in human fetuses in their undisturbed environment. Using this technique, we have obtained preliminary data which indicate that cardiac contractility and output indexed to fetal size is not significantly different in asymmetrical IUGR fetuses when compared to normal fetuses. We hypothesize as a result of these observations that differences in regional blood flows must occur in the human fetus affected by asymmetrical IUGR. We hypothesize that an alteration in blood flow to kidneys and lower limbs will occur early in fetuses affected by IUGR, but flow to the middle cerebral artery will be maintained and as such, ALTERATION in the study of regional blood flow could be used as an early marker for IUGR. Color pulsed Doppler will help to visualize small vascular structures and to quantify blood flow to the leg, kidney and brain of 50 normal human fetuses and in 50 fetuses with asymmetrical IUGR. These Doppler examinations will be started at around the 18th to 20th week of gestation and repeated every four weeks until delivery. Ultrasound measurements of the fetal head, abdomen and femur will be obtained at each Doppler examination. Pulsed Doppler will also be used to calculate right and left ventricular output. We will also document if such alteration in regional blood flow PRECEDES or is CONTEMPORANEOUS with the abnormal somatic growth and will document the time onset of this blood flow decrease. We anticipate that changes in regional blood flow will occur prior to ultrasound confirmation of decreased growth. A complete understanding in the distribution of regional blood flow in the human fetus at risk for asymmetrical IUGR may in turn lead to an earlier diagnosis of such pathological conditions and may permit early intervention. Such intervention may in turn decrease the morbidity/mortality associated with IUGR fetuses.